It's a bit of an obsolete example these days, but think back and consider cigarette advertising, and someone trying to quit. If you just blocked them out, marketers would evolve new ways to reach you, right? But if their logos and ads were always surrounded by a picture-border of pulsing blackened lung-samples... Well, you're actually reprogramming your own mind to dislike their brand, which is very different.
A tamer example would be to enhance your recognition of "good" brands at the expense of the bad/less-good ones. Imagine walking through a supermarket and having your eye drawn to the "good" products at the expense of the "bad" ones. (Where Good/Bad is determined by some criteria that are resistant to subconscious advertising.)
so what are those criteria, and more importantly, how much bribery would advertisers/companies pay to make themselves on the good list?
Negative advertising is just as bad as positive advertising in the scenario you proposed.
The most important difference is it helps increase your ability to control your own unthinking behavior through other conscious choices. (This is generally agreed to be a worthwhile thing, and factors prominently in a lot of religious and psychological traditions.)